Microwave motion detectors having a microwave transceiver are able to detect the existence of a moving object, such as an intruder, in an area monitored by the motion detector.
Generally, the motion detector transmits a microwave signal toward the detection area and in the event that a moving object passes through the monitored area, the microwave signal is reflected back (echo) from such movement and is modulated due to the Doppler Effect. When a signal is reflected from a moving object, it is shifted in frequency. The shift in frequency is called the Doppler Effect and is directly proportional to the target velocity. Typically, a maximum frequency shift occurs when the object is moving straight towards the sensor and a minimum frequency shift occurs when the object is moving at 90 degrees orthogonal to the sensor. All Doppler sensors use this principle to detect moving objects in the detection area.
Traditionally, the microwave sensors are built to have a cavity transceiver to meet the operational requirement of the sensor on high frequency bands, such as a K-band. In the waveguide-cavity-based transceiver, the microwave signal is generated from a waveguide cavity oscillator using suitable diode, and the receiver has similar waveguide structure to receive the reflected signals. Due to the complex assembling and high power consumption, planar microwave circuit has been developed to substitute the waveguide structure, especially those waveguide sensors used in the civil field.
However, the existing microwave planar sensors have disadvantages with respect to their packaging processes and electromagnetic shielding. Traditionally, microwave circuits used in the microwave planar sensors are shielded through either metal casting process or metal stamping process, each of which exhibits undesirable disadvantages.
In the metal casting process, firstly an initial cost for breaking a mould is inevitable, which is normally expensive. In addition, due to the fact that the soldering techniques are not applicable to metal casting, conductive adhesives are necessary for physically and electrically connecting the metal components of the circuits to the PCB board. The conductive adhesives consist of silver paste for implementing the electrical connection, which in turn significantly raises the cost of the adhesives as well as the entire sensor. Moreover, the application of the conductive adhesives is laborious and requires certain proficiency of the workers, unless a designated adhesive-applying machine is used, which again increases the manufacturing cost and further does not provide the compatibility of working on different designs. In addition, the metal casting processes require a curing time after applying the conductive adhesives, which results in prolonging of manufacturing and low production efficiency. Last, the structure strength of the connection implemented by conductive adhesives is not satisfactory, especially when the sensor is used under critical circumstances. Thus, the failure of the sensor due to the breaking of the connection may happen.
In the metal stamping process, consistency of the critical geometrical parameters of the sensor cannot be maintained due to the inherent deficiency of metal stamping with regard to its accuracy and precision. However, the consistency of the dimensions of the device components and the accuracy of the positional relationship between the different components play a critical role for implementing the functionality of the sensor, in that any structural deviation of the sensor may cause a shift in the frequency of the signal, especially in high frequency bands. In addition, in order to facilitate metal stamping, soft metallic materials are normally adopted, which produces a basic enclosing structure with thin-walls made of soft metallic materials, such as the resonant cavity. Thus, it is difficult to further incorporate tuning structures on the stamped parts in order to enhance the performance of the sensor and expand the applications of the sensor.
Moreover, the above-discussed processes pose another problem that the microwave circuits of the sensors are not electromagnetically shielded satisfactorily. Thus, electromagnetic interference with environmental signal may happen, which would impact the performance and reliability of the sensors.
Practically, microwave sensors used in security industry are usually secured at a predetermined location, such as a wall, to scan a predetermined coverage area. Thus, the detecting scope of a sensor is fixed, once the sensor is secured to the wall. In case the application circumstances of the sensor require adjusting the detecting scope, the angle between the sensor and the wall has to be changed by either remounting the sensor in the case to assume a new desirable orientation or changing the relative positions between the wall and the sensor case. Furthermore, in some cases, the detecting angle has to be tuned more or less depending on the specific application of the sensor, so as to realize the best performance of the sensor. Thus, it is desirable to avoid the complex and laborious procedures in the art to adjust the detecting angle of the sensor.
Thus, it would be desirable and advantageous to provide a microwave planar sensor, which is capable of saving manufacturing costs by excluding conductive adhesives with silver paste.
Thus, it would be desirable and advantageous to provide a microwave planar sensor, which is capable of improving the reliability of the connection between the metal components of the circuits and the PCB board.
Thus, it would be desirable and advantageous to provide a microwave planar sensor, which is capable of cutting down the time incurred in the manufacturing process and lowering the proficiency requirement for the workers in the production line, thereby improving production efficiency.
Thus, it would be desirable and advantageous to provide a microwave planar sensor, which is capable of maintaining a geometrical consistency of the physical structures of the sensor, thereby improving the performance of the sensor.
Thus, it would be desirable and advantageous to provide a microwave planar sensor, which is capable of tuning or adjusting the detecting angle of the sensor, thereby providing a sensor with improved resilience and compatibility.
Thus, it would be desirable and advantageous to provide a microwave planar sensor, which is capable of providing a satisfactory electromagnetic shielding for the microwave circuits, so as to prevent the microwave circuits from being interfered with the environment signals and noises within the vicinity of the microwave circuits.